In recent years, liquid crystal display panels, a class of panels that use electro-optical conversion materials, have come into wide use as display means for displaying various kinds of information on portable electronic apparatus such as notebook computers, mobile telephones, and wrist watches. In particular, in a portable electronic apparatus or the like, the liquid crystal panel is accommodated in a limited space inside the apparatus housing. Further, in such a portable electronic apparatus, there is a need to increase the amount of information that can be displayed, and it is therefore desired to provide a construction that maximizes the display area and minimizes the area outside the display area (in this patent specification, such an outside area is hereinafter sometimes referred to as the “non-display area” or the “peripheral portion”).
In this type of display apparatus and, in particular, in a display apparatus called the passive matrix (direct matrix) type, a liquid crystal material is sealed between two substrates, and stripe-shaped electrodes intersecting at right angles to each other are formed on the opposing surfaces of the substrates. In this type of display apparatus, pixels are formed at the positions where the electrodes on the two substrates intersect each other, and a method is employed that drives the liquid crystal, on a pixel-by-pixel basis, from the outside. To drive the liquid crystal by using the electrodes disposed opposite each other, it has been practiced to mount a driver IC in the non-display area of each substrate and form, in the same area, wiring lines for electrically connecting the electrodes to the terminals of the driver IC. Accordingly, each substrate protrudes outwardly beyond the other substrate.
This structure, however, has had the problem that the peripheral portion becomes large because an area for mounting the driver IC has to be provided on each substrate. Furthermore, the shape of the liquid crystal display panel becomes asymmetric with either the left or right side or either the upper or lower side greatly extending outward relative to the other side. When mounting such a liquid crystal panel, for example, inside the housing of a portable electronic apparatus, there has arisen the problem that the panel cannot be accommodated unless the outer frame of the housing is made larger. The further problem has been that, since the outer frame of the housing has to be made asymmetric in shape, the liquid crystal display section cannot be placed in the center of the electronic apparatus.
In view of the above situation, a method that drives the liquid crystal by a single driver IC has been proposed for a small-size panel having a moderate number of pixels, such as a panel for a mobile telephone, for such purposes as reducing the peripheral portion area of the liquid crystal display panel, making the peripheral portion shape symmetrical, and reducing the number of driver ICs used (for example, Patent Document 1: Japanese Unexamined Patent Publication No. 2003-98532).
In this driving method, all the electrodes formed on the two substrates are electrically connected to a large number of wiring lines formed on the non-display area of one substrate, and these wiring lines are connected to the single driver IC.
FIG. 13 shows an example in which the liquid crystal panel is driven by a single driver IC as described above. In FIG. 13, the driver IC 7 is mounted on the upper surface of the lower substrate 2, and a large number of stripe-shaped signal electrodes 10 are formed on the same surface. The signal electrodes 10 are connected to the corresponding terminals of the driver IC 7 via a large number of wiring lines 15.
On the other hand, a large number of stripe-shaped driving electrodes 11 are formed on the lower surface of the upper substrate 3 in such a manner as to intersect at right angles with the signal electrodes 10. Of the driving electrodes 11 (10 driving electrodes 11 are shown in FIG. 13), the driving electrodes 11-1 to 11-5 in the upper half of the figure (the upper five electrodes in FIG. 13) are connected at their right ends to transfer-connection positions T1 to T5 where connections are made to a conductive seal member 16b. A portion H encircling the transfer-connection positions T1 to T5 in FIG. 13 is shown in enlarged form in FIG. 14. As shown in FIG. 14, the transfer-connection positions T1 to T5 are located on extended lines Q to which the respective driving electrodes 11-1 to 11-5 are extended in straight lines.
The driving electrodes 11-1 to 11-5 formed on the lower surface of the upper substrate 3 are electrically connected at the respective transfer-connection positions T1 to T5 on the seal member 16b to driving electrode wiring lines 14 formed on the upper surface of the lower substrate 2. These wiring lines 14 are connected to output terminals (not shown) of the driver IC 7 mounted on an extended portion 9 of the lower substrate 2. The conductive seal portion 16b of the seal member 16 is formed from an anisotropic conductive adhesive prepared by mixing electrically conductive particles into an insulating adhesive resin. Accordingly, the driving electrodes 11-1 to 11-5 connected to the conductive seal portion 16b are electrically connected to the respective wiring lines 14 via an inter-substrate conducting portion formed by the electrically conductive particles.
Likewise, the driving electrodes 11-6 to 11-10 in the lower half of FIG. 13 (the lower five electrodes in FIG. 13) are connected at their left ends to transfer-connection positions T6 to T10 where connections are made to a conductive seal member 16a. A portion I encircling the transfer-connection positions T6 to T10 in FIG. 13 is shown in enlarged form in FIG. 15. As shown in FIG. 15, the transfer-connection positions T6 to T10 are located on extended lines Q to which the respective driving electrodes 11-6 to 11-10 are extended in straight lines.
The driving electrodes 11-6 to 11-10 formed on the lower surface of the upper substrate 3 are electrically connected at the respective transfer-connection positions T6 to T10 on the seal member 16a to driving electrode wiring lines 14 formed on the upper surface of the lower substrate 2. These wiring lines 14 are connected to output terminals (not shown) of the driver IC 7 mounted on the extended portion 9 of the lower substrate 2. Here also, the conductive seal portion 16a of the seal member 16 is formed from an anisotropic conductive adhesive prepared by mixing electrically conductive particles into an insulating adhesive resin. Accordingly, the driving electrodes 11-6 to 11-10 connected to the conductive seal portion 16a are electrically connected to the respective wiring lines 14 via an inter-substrate conducting portion formed by the electrically conductive particles.
In this way, the driving electrodes 11 on the upper substrate 3 and the signal electrodes 10 on the lower substrate 2 are all connected to the corresponding terminals of the driver IC 7 mounted on the lower substrate 2, and image signals and operation signals are supplied from this driver IC 7 to all the signal electrodes 10 and driving electrodes 11.
That is, in the example shown in FIG. 13, the wiring lines 14 to the driving electrodes 11 are formed on the lower substrate 2. Further, the driving electrodes 11 are formed so as to be transfer-connected to the wiring lines 14 on the extended lines Q to which the respective driving electrodes 11 are extended in straight lines.
The prior art also proposes a display apparatus that employs a resistance ratio adjusting technique in which the wiring resistance ratio between the wiring lines connecting to the driving electrodes is reduced by routing the wiring lines in such a manner as to return in the reverse direction at one side of the display area, thereby reducing the unevenness of display (a phenomenon in which the display brightness differs between one portion of the display area and the other portion thereof) that can occur when the wiring resistance ratio is large (for example, Patent Document 2: Japanese Unexamined Patent Publication No. 2002-148654).
In the prior art, it is also known to provide a display apparatus that employs a configuration in which the scanning lines formed on the inside surface of the opposite substrate are electrically connected via a seal member to the wiring lines formed on the upper surface of a device substrate, at positions other than the positions on the extended lines to which the scanning lines are extended in straight lines (for example, Patent Document 3: Japanese Unexamined Patent Publication No. 2003-29289).
As described above, the trend in recent display apparatuses is toward increasing the display capacity more than ever. If the display capacity (the number of pixels) of display apparatus increases, the number of wiring lines increases, requiring a larger area for the formation of the wiring lines.
One possible method for preventing the area necessary for the formation of the wiring lines 14 from increasing despite the increase of the display capacity would be to reduce the pitch of the wiring lines 14. For example, in the display apparatus described in Patent Document 1, the line/space (L/S) of the wiring lines 14 is chosen to be about 22/10 μm, and the width of each wiring line 14 is chosen to be about 22 μm.
In the display apparatus described in Patent Document 1, the wiring lines 14 to the driving electrodes 11 are formed on the lower substrate 2, and the driving electrodes 11 are transfer-connected to the wiring lines 14 on the straight extended lines (extended lines Q) of the driving electrodes 11, as earlier described. Furthermore, as the driving electrodes 11 are brought out laterally in straight lines, the routing lengths of the wiring lines 14 increase, increasing the difference in wiring resistance between the wiring lines 14 and causing unevenness and crosstalk in the displayed image, hence the problem of display quality degradation.
FIG. 16 shows the relationship, G, of the normalized wiring resistance Ω (ohm) to the arrangement numbers N (1 to 10 lines) of the driving electrodes 11. The driving electrodes 11-1 to 11-5 in FIG. 13 correspond to the arrangement numbers 1 to 5 in FIG. 16, while the driving electrodes 11-6 to 11-10 correspond to the arrangement numbers 6 to 10 in FIG. 16. In FIG. 13, the driving electrode 11-1 is nearest to the driver IC 7, so that the length of its wiring line 14 is short and the wiring resistance is therefore low. On the other hand, the driving electrode 11-10 in FIG. 13 is farthest from the driver IC 7, so that the length of its wiring line 14 is long and the wiring resistance is therefore high.
Here, of the wiring lines (shown in the upper right of FIG. 13) for the driving electrodes 11-1 to 11-5, the wiring line for the driving electrode 11-1 nearest to the driver IC 7 is formed on the outer side, while the wiring line for the driving electrode 11-5 farthest from the driver IC 7 is formed on the inner side. On the other hand, of the wiring lines (shown in the upper and lower right of FIG. 13) for the driving electrodes 11-6 to 11-10, the wiring line for the driving electrode 11-6 nearest to the driver IC 7 is formed on the outer side, while the wiring line for the driving electrode 11-10 farthest from the driver IC 7 is formed on the inner side. The reason for this arrangement is that any wiring line must be routed without crossing any other wiring line. Accordingly, a large difference occurs in terms of distance between the wiring line for the driving electrode 11-5, which is routed along the inner side, and the wiring line for the driving electrode 11-6, which is routed along the outer side. This difference results in a wiring resistance step between the driving electrode arrangement numbers 5 and 6 in FIG. 16.
With the driving electrode (for example, 11-1) whose wiring resistance is low, a sufficiently high driving voltage is applied to the liquid crystal but, in the case of the driving electrode (for example, 11-10) whose wiring resistance is high, the applied driving voltage drops. Here, if the driving voltage decreases gradually and uniformly from the upper to the lower of FIG. 13, no appreciable problem will occur in the display quality of the display panel as a whole. However, if there is a portion where the wiring resistance changes greatly, as shown in the wiring resistance graph G of FIG. 16, an appreciable difference occurs in terms of display quality before and after that portion. More specifically, in the example of FIG. 13, there has been the problem that the display quality degrades because a border becomes visible between the upper half, where display operation is controlled by the driving electrodes 11-1 to 11-5, and the lower half, where display operation is controlled by the driving electrodes 11-6 to 11-10.
Further, in the display apparatus disclosed in Patent Document 1, the seal member 16 has a dual seal structure consisting of a conductive seal member and an insulating seal member, and the wiring lines are placed under the insulating seal member. Patent Document 1 describes that, with this structure, a compact and thin-peripheral portion panel can be achieved by eliminating the wiring line formation area traditionally provided outside the seal. However, the double seal structure has had the problem that the manufacturing process becomes complex and the cost increases.
Furthermore, in the display apparatus disclosed in Patent Document 1, the wiring lines 14 to the driving electrodes 11 are formed on the lower substrate 2. Further, the ends of the driving electrodes 11 are brought out in a direction orthogonal to the direction of the signal electrodes 10, and the driving electrodes 11 are transfer-connected at their ends to the respective wiring lines 14. There has, therefore, been the problem that the space surrounding the signal electrodes (the space bounding the sides of the signal electrodes) opposite the end portions of the driving electrodes 11 cannot be used at all because the end portions of the driving electrodes 11 are used exclusively for the above purpose.
In the display apparatus disclosed in Patent Document 2, the resistance ratio between the wiring lines is adjusted by routing the wiring lines in such a manner as to return in the reverse direction at one side of the display area. As the wiring lines are routed back and forth, a large area for accommodating the wiring lines has had to be provided in the side portion of the display area; thus, the display apparatus has had the problem that the peripheral portion area, and hence the overall size of the display apparatus, cannot be reduced.
Further, in the display apparatus disclosed in Patent Document 2, since the wiring lines are transferred to the opposite substrate via the side portion of the seal member on the driver IC side, the area of the seal member has had to be increased in order to ensure the electrical conduction area of the transfer portion (i.e., to ensure the reliability of electrical conduction). Accordingly, the ratio of the peripheral portion (non-display) area to the display area becomes large, leading to the problem that the reduction of the display apparatus size cannot be expected and, not only that, otherwise unnecessary substrate, and other, material costs occur in the manufacturing process.
In the display apparatus disclosed in Patent Document 3, the driving electrodes are brought out at one or the other end thereof in alternating fashion, and are transfer-connected to the corresponding wiring lines at positions displaced from the extended lines of the respective driving electrodes. However, as the driving electrodes are brought out for transfer connection at one or the other end thereof in alternating fashion, there has been the problem that the areas at the ends of the driving electrodes cannot be effectively utilized. Furthermore, the display apparatus disclosed in Patent Document 3 has had the problem that the resistance values of the wiring lines cannot be corrected because the positions at which the driving electrodes are transfer-connected to the wiring lines are always displaced in the same direction from the extended lines of the driving electrodes.